Module for raster to vector conversion.
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<h3>Inputs</h3>
<ul>      
<li>the raster that has to be converted</li>
<li>the value to use to trace the polygons, if it is null then all the values of the raster are used</li>
<li>the field name to use as to store the raster value in the vector</li>
<li>a threshold on cell number to filter away polygons with cells less than that</li>
</ul>
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<h3>Output</h3>
<ul>      
<li>the extracted vector</li> 
</ul>